So I picked up a Crate GX-140CH REALLY cheap because it wouldn't change channels. Only the overdrive channel worked. When I got it home and had a chance to really test it out I found:
The front panel channel switch showed the correct lit red LED when set to the overdrive channel and sounded fine, but when set to the clean channel via the front panel switch only silence and the green LED was dark. With the foot switch it was same.
The over drive channel has two "drive" settings. They switched fine on the front panel and via the foot switch.
The chorus was "stuck" on regardless of the front panel or foot switch setting.
I found the schematics (attached) and I figured out that all the switching went through the foot switch jacks regardless of if you used the foot switch on front panel or the foot switch. Note that the foot switch defeats the front panel switches. I gave the foot switch jacks a good cleaning and the chorus now worked correctly with the front panel and foot switch!
Since the clean channel was still MIA I tore it apart. I found that I was not the first person in it. Someone had messed with Q16, which appears to be the channel switching BJT as well as other seemingly random bad looking solder joints. There was nothing left of the base PCB pad of Q16. It is a MPS-A55 so I don't know if it is original or a replacement, but who ever did the "work" really butchered it, even by my standards (). I jumpered around the bad pad and clean up a few other areas that appeared to have been messed with and found another couple of bad pads/junctions and jumpered around them. I reflowed and added a little more solder on a few other iffy looking spots as well as all of the jacks, pots and switches on the preamp PCB. I never removed the power amp PCB since the issue seemed to be with the preamp board since all of the switching appears to be handed there with the exception of the traces which run to the foot switch jacks. The preamp and power amp board are connected via a multi-connector cable.
I put it back together and tested. Viola! The clean channel works and all of the front switches work as they should. I tried the foot switch and the channels switch as they should, but I noticed that the red LED only come on VERY dim, if at all, when the overdrive channel is selected with the foot switch. The LED on the foot switch lights correctly and the green panel LED lights when the clean channel is on. Hmm. So I test the foot switch with a Crate Blue Voodoo and it works fine with that amp. I try another foot switch I have laying around without an LED and the front panel LED lights act correctly. If the TRS foot switch cable is plugged into the amp but not plugged into the foot switch itself the drive channel is activated and the red LED on the front panel light.
I'm kind of stumped. Am I losing voltage to the front panel LED somewhere when the foot switch is activated? Any ideas?
53101H2_.pdf
443XXC3.pdf
The front panel channel switch showed the correct lit red LED when set to the overdrive channel and sounded fine, but when set to the clean channel via the front panel switch only silence and the green LED was dark. With the foot switch it was same.
The over drive channel has two "drive" settings. They switched fine on the front panel and via the foot switch.
The chorus was "stuck" on regardless of the front panel or foot switch setting.
I found the schematics (attached) and I figured out that all the switching went through the foot switch jacks regardless of if you used the foot switch on front panel or the foot switch. Note that the foot switch defeats the front panel switches. I gave the foot switch jacks a good cleaning and the chorus now worked correctly with the front panel and foot switch!
Since the clean channel was still MIA I tore it apart. I found that I was not the first person in it. Someone had messed with Q16, which appears to be the channel switching BJT as well as other seemingly random bad looking solder joints. There was nothing left of the base PCB pad of Q16. It is a MPS-A55 so I don't know if it is original or a replacement, but who ever did the "work" really butchered it, even by my standards (). I jumpered around the bad pad and clean up a few other areas that appeared to have been messed with and found another couple of bad pads/junctions and jumpered around them. I reflowed and added a little more solder on a few other iffy looking spots as well as all of the jacks, pots and switches on the preamp PCB. I never removed the power amp PCB since the issue seemed to be with the preamp board since all of the switching appears to be handed there with the exception of the traces which run to the foot switch jacks. The preamp and power amp board are connected via a multi-connector cable.
I put it back together and tested. Viola! The clean channel works and all of the front switches work as they should. I tried the foot switch and the channels switch as they should, but I noticed that the red LED only come on VERY dim, if at all, when the overdrive channel is selected with the foot switch. The LED on the foot switch lights correctly and the green panel LED lights when the clean channel is on. Hmm. So I test the foot switch with a Crate Blue Voodoo and it works fine with that amp. I try another foot switch I have laying around without an LED and the front panel LED lights act correctly. If the TRS foot switch cable is plugged into the amp but not plugged into the foot switch itself the drive channel is activated and the red LED on the front panel light.
I'm kind of stumped. Am I losing voltage to the front panel LED somewhere when the foot switch is activated? Any ideas?
53101H2_.pdf
443XXC3.pdf
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